华北背景地区有机气溶胶类型及其形成与化学演变特征研究

Organic aerosol (OA) comprises a large fraction (20-90 %) of the submicron particulate mass. In China, OA also occupies about one half of fine particles(PM1).Given the complex chemical composition, multitude of sources, and complex processing, OA is one of the least understood components of ambient aerosols. Models are generally unsuccessful in reproducing the observed magnitudes and variability of these particles. Such difficulties likely arise from complexity in the sources, composition, and chemistry of OA. New particle formation is the beginning of aerosol evolution, but nucleation mechanisms that involve organics have not yet been identified. Thus, characterization of the sources, composition, and concentration of ambient OA, along with OA formation and transformation processes, is important. However, OA sources, formation，atmospheric processing are very uncertain now..In order to better understand the sources, composition and evolution of organic aerosols, a high time resolution Q-AMS (aerosol mass spectrometer) is to be employed to measure the ensemble mass concentrations of organic matter. Positive matrix factorization (PMF) will be performed on a subset of components to identify major sources of submicron OA at the regional background site (Shang Dianzi) in Northern China. From the fraction of m/z 44 (CO2+) and m/z 43(mostly C2H3O+), atomic oxygen-carbon ratio (O/C) ratio and Hydrogen-carbon (H/C) ratio can be calculated for these different types of organic aerosols. In this study, we will investigate the evolution process of total OA from these compositional characteristics by using a Van Krevelen diagram. .Considering the limitation of AMS to get the chemical components information in small size particles accurately, transmission electron microscopy (TEM) is introduced to identify the chemical and physical characterization of individual aerosol particles during typical new particle formation events. The elemental composition, size distribution and mixture states for nano-particles can be determined by TEM coupled with energy-dispersive X-ray spectrometer (EDS). Combining TEM analysis with AMS data, the importance of different components (sulfuric acid or secondary organic compounds) contributed to the particle nucleation and growth will be discussed in this study..These results are very necessary to thorough understand the sources, formation and evolution of organics. It is also significant for improving air quality model, SOA model and climate change model.

本研究拟利用高时间分辨率观测仪器气溶胶质谱仪（Q-AMS），对我国华北区域代表性站点（上甸子）开展亚微米气溶胶化学组份质量谱观测实验。利用正矩阵因子分析方法，对AMS观测数据进行有机气溶胶来源类型解析；从AMS数据中提取并计算出不同类型有机气溶胶的H:C和O:C数据，从两者的关系中探讨有机气溶胶在大气中的氧化途径和演变特点；利用透射电镜（TEM）分析方法，对膜采样获得的气溶胶进行单颗粒分析，配合AMS在线观测数据，探究不同化学组份（尤其是硫酸盐、有机物）在新粒子形成、增长/老化过程中的作用。这为了解我国华北区域有机气溶胶的来源类型、形成、演变过程，改善空气质量模式、SOA模式和气候变化模式有重要科学意义。

本研究项目利用高时间分辨率观测仪器气溶胶质谱仪（Q-AMS），对我国长三角区域代表性站点（临安）开展亚微米气溶胶化学组份质量谱连续两年的观测实验。从高时间分辨率观测数据出发，结合正矩阵因子分析（PMF）手段，从AMS 的质谱中提取特征性质量碎片,将气相中奇氧（Ox=O3+NO2）和一氧化碳（CO）分别作为城市大气污染老化过程和一次燃烧排放源示踪剂，确定有机气溶胶因子个数，识别不同因子的主要来源，获得区域站点有机气溶胶的来源类型。根据观测数据和经验公式绘制Van Krevelen图，探讨有机物的演变过程。利用透射电镜（TEM）分析方法，对膜采样获得的气溶胶进行单颗粒分析，配合AMS 在线观测数据，探究不同化学组份（尤其是硫酸盐、有机物）在新粒子形成、增长/老化过程中的作用。.该项目利用PMF方法结合特定示踪剂，将有机气溶胶（OA）解析出低挥发性有机气溶胶（LV-OOA），半挥发性有机气溶胶（SV-OOA），生物质燃烧类有机气溶胶（BBOA）和碳氢类有机气溶胶（HOA）。其中，LV-OOA平均浓度为13 μg/m3，约占总有机气溶胶的44 %，BBOA 约占OA的25 %, HOA和SV-OOA 分别占OA的22%和9.3%。.项目总结出临安四季有机气溶胶老化是以不破坏C-C键，而是在CH2上加成OH和C=O或OH和COOH为主要特征的氧化途径。在结合AMS观测数据与透射电镜分析手段对新粒子生成事件的研究中发现，一次排放的飞灰，金属颗粒和二次转化的硫酸盐可能充当了粒子成核的主要成分，粒子增长和老化阶段，挥发性有机物在原有一次排放和二次转化颗粒物表面凝结增长，黑炭和金属粒子与环境大气中的气体、水汽等发生非均相反应是粒子增长的主要途径。.以上研究成果对于揭示环境大气中有机气溶胶的来源类型、形成、演变过程，改善空气质量模式，SOA 模式和气候变化模式的预报能力有重要意义。